A(1). Field of the invention
The invention relates to a receiver, particularly for use in a digital telecommunication system, which is arranged for receiving a line signal formed by a first digital signal, encoded in a line code and representing a digital version of an analog information signal, the receiver comprising:
an input for receiving said line signal;
a decoder coupled to said input and arranged for converting the line signal into said first digital signal
a digital-to-analog converter comprising an input;
means for coupling the input of the digital-to-analog converter to the receiver input.
A(2). Description of the prior art
In recent years high-speed digital base band transmission over existing coaxial cables has received a great deal of interest. Due to their particular structure coaxial cables provide high transmission quality. These cables are substantially immune to crosstalk and impulse interferences. Thermal noise being generated by the cable itself as well as by the associated equipment such as equalisers and amplifiers in the regenerative repeaters is usually the major source of interference to the pulses of the pulse signal to be transmitted. Another quantity which must be taken into consideration is the low-frequency cut-off of the transmission path due to the inductive or capacitive coupling of the cable to the signal sources. To prevent the digital signal applied to the cable from having relevant frequency components which are lower than the low-frequency cut-off frequency, it is customary to subject the digital signal to be transmitted, before it is applied to the cable, to a coding method, whereby a digital signal is obtained in a so-called line code (see the reference in paragraph D). The last-mentioned signal will be denoted the line signal hereinafter.
Apart from the fact that the line signal does not contain frequency components which are lower than the said low-frequency cut-off frequency, the line code is usually chosen so that the line signal has more 0-1 transitions than the original signal, so that clock extraction and regeneration can be done in a simple manner.
Although the transmission quality of the existing cables is very good, bit errors can still be produced by external influences. These errors are audible irrespective of whether the first digital signal is a pulse code modulated signal or a delta modulation signal. A delta modulation signal is indeed less sensitive to bit errors than a pulse code modulated signal, but, particularly, "error bursts", that is to say multiple errors such as sequences of identical bits, resulting from protractedly dominating noise pulses in a transmission medium are very annoying, even with delta modulation.